Drive transmission unit and image forming apparatus incorporating same

ABSTRACT

A drive transmission unit is described that includes a drive source, and a rotatable drive transmitting member to transmit a driving force from the drive source. The drive transmitting member includes a bottom part intersecting an axis of the drive transmitting member, a circular transmitting part extending from the bottom part in an axial direction of the drive transmitting member and including an internal toothed surface on an inner circumferential surface of the transmitting part to mesh with a first member, and a first projecting part and a second projecting part projecting in opposite directions from the bottom part along the axial direction of the drive transmitting member and having different diameters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application Nos. 2014-062083, filedon Mar. 25, 2014, and 2015-006718, filed on Jan. 16, 2015, in the JapanPatent Office, the entire disclosure of each of which is herebyincorporated by reference herein.

BACKGROUND

Technical Field

Embodiments of this disclosure generally relate to a drive transmissionunit and an image forming apparatus incorporating the drive transmissionunit.

Background Art

Various types of electrophotographic image forming apparatuses areknown, including copiers, printers, facsimile machines, andmultifunction machines having two or more of copying, printing,scanning, facsimile, plotter, and other capabilities. Such image formingapparatuses usually form an image on a recording medium according toimage data. Specifically, in such image forming apparatuses, forexample, a charger uniformly charges a surface of a photoconductorserving as an image carrier. An optical writer irradiates the surface ofthe photoconductor thus charged with a light beam to form anelectrostatic latent image on the surface of the photoconductoraccording to the image data. A developing device supplies toner to theelectrostatic latent image thus formed to render the electrostaticlatent image visible as a toner image. The toner image is thentransferred onto a recording medium directly, or indirectly via anintermediate transfer belt. Finally, a fixing device applies heat andpressure to the recording medium carrying the toner image to fix thetoner image onto the recording medium.

Such image forming apparatuses may incorporate a number of drivers anddrive transmission units to operate the photoconductor, the transferbelt, and the like.

SUMMARY

In one embodiment of this disclosure, a novel drive transmission unit isdescribed that includes a drive source, and a rotatable drivetransmitting member to transmit a driving force from the drive source.The drive transmitting member includes a bottom part intersecting anaxis of the drive transmitting member, a circular transmitting partextending from the bottom part in an axial direction of the drivetransmitting member and including an internal toothed surface on aninner circumferential surface of the transmitting part to mesh with afirst member, and a first projecting part and a second projecting partprojecting in opposite directions from the bottom part along the axialdirection of the drive transmitting member and having differentdiameters.

Also described is an image forming apparatus incorporating the drivetransmission unit.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be more readily obtained as the same becomesbetter understood by reference to the following detailed description ofembodiments when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic sectional view of an image forming apparatusaccording to an embodiment;

FIG. 2A is a schematic sectional view of a drive transmission unitaccording to a first embodiment;

FIG. 2B is a vertical sectional view of the drive transmission unitalong a line shown in FIG. 2A;

FIG. 3 is a schematic sectional view of a drive transmission unitaccording to a second embodiment;

FIG. 4 is a schematic sectional view of a drive transmission unitaccording to a third embodiment;

FIG. 5 is a schematic sectional view of a drive transmission unitaccording to a fourth embodiment;

FIG. 6A is a schematic sectional view of a drive transmission unitaccording to a fifth embodiment;

FIG. 6B is a vertical sectional view of the drive transmission unitalong a line shown in FIG. 6A; and

FIG. 7 is a schematic sectional view of a comparative drive transmissionunit.

The accompanying drawings are intended to depict embodiments of thisdisclosure and should not be interpreted to limit the scope thereof.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that have the samefunction, operate in a similar manner, and achieve similar results.

Although the embodiments are described with technical limitations withreference to the attached drawings, such description is not intended tolimit the scope of the invention and not all of the components orelements described in the embodiments of this disclosure areindispensable.

In a later-described comparative example, embodiment, and exemplaryvariation, for the sake of simplicity like reference numerals are givento identical or corresponding constituent elements such as parts andmaterials having the same functions, and redundant descriptions thereofare omitted unless otherwise required.

It is to be noted that, in the following description, suffixes Y, C, M,and Bk denote colors yellow, cyan, magenta, and black, respectively. Tosimplify the description, these suffixes are omitted unless necessary.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views,embodiments of this disclosure are described below.

Initially with reference to FIG. 1, a description is given of an imageforming apparatus 1 according to an embodiment of this disclosure. FIG.1 is a schematic sectional view of the image forming apparatus 1.

As illustrated in FIG. 1, the image forming apparatus 1 includes, e.g.,an exposure device 2, an image forming device 3, a transfer device 4, asheet feeder 5, a conveyance passage 6, a fixing device 7, and anejection device 8.

The exposure device 2 is positioned in an upper portion of the imageforming apparatus 1, and includes a light source that emits, e.g., laserbeams and various optical systems. Specifically, the exposure device 2irradiates a photoconductor 32 of the image forming device 3, describedlater, with laser beams for each color separation component of an imagecreated according to image data received from an image acquisitiondevice, thereby exposing the surface of the photoconductor 32.

The image forming device 3 is positioned below the exposure device 2,and includes a plurality of process cartridges 31 removable from theimage forming apparatus 1. Each of the process cartridges 31 includes,e.g., a drum-shaped photoconductor 32 capable of bearing toner asdeveloper on its surface, a charging roller 33 that uniformly chargesthe surface of the photoconductor 32, a developing device 34 thatsupplies toner to the surface of the photoconductor 32, and aphotoconductor cleaning blade 35 that cleans the surface of thephotoconductor 32.

The process cartridges 31 includes four process cartridges 31Y, 31C,31M, and 31Bk for four different colors of yellow, cyan, magenta, andblack, respectively, which are color separation components of a colorimage. The four process cartridges 31 are identical in configuration,differing only in the color employed. To simplify the description, thesesuffixes are omitted unless necessary.

The transfer device 4 is positioned under the image forming device 3.The transfer device 4 includes, e.g., a drive roller 41, a driven roller42, an endless intermediate transfer belt 43 entrained rotatably aroundthe drive roller 41 and the driven roller 42, a cleaning blade 44 thatcleans an outer circumferential surface of the intermediate transferbelt 43, four primary transfer rollers 45 facing the respectivephotoconductors 32 of the process cartridges 31 via the intermediatetransfer belt 43, and a secondary transfer roller 46. Each of the fourprimary transfer rollers 45 presses an inner circumferential surface ofthe intermediate transfer belt 43 against the correspondingphotoconductor 32 to form a contact area called a primary transfer nipbetween the intermediate transfer belt 43 and the photoconductor 32.

The secondary transfer roller 46 faces the drive roller 41 via theintermediate transfer belt 43, and presses the outer circumferentialsurface of the intermediate transfer belt 43 against the drive roller 41to form a contact area called a secondary transfer nip between theintermediate transfer belt 43 and the secondary transfer roller 46.

A waste toner container 47 is disposed below the intermediate transferbelt 43 to receive, through a waste toner conveying tube, waste tonerremoved from the intermediate transfer belt 43 by the cleaning blade 44.

The sheet feeder 5 is positioned in a lower portion of the image formingapparatus 1, and includes, e.g., a tray 51 that accommodates recordingmedia P, and a sheet feeding roller 52 that picks up the recording mediaP from the tray 51.

The recording media P are conveyed through the conveyance passage 6 fromthe sheet feeder 5 toward the ejection device 8. Pairs of conveyancerollers including a pair of registration rollers 61 are disposed alongthe conveyance passage 6.

The fixing device 7 includes, e.g., a heater 71, a fixing roller 72heated by the heater 71, and a pressing roller 73 capable of pressingthe fixing roller 72.

The ejection device 8 is disposed at the most downstream position of theconveyance passage 6. The ejection device 8 includes a pair of ejectionrollers 81 that ejects the recording media P outside, and an ejectiontray 82 that receives the recording media P ejected by the pair ofejection rollers 81.

With continued reference to FIG. 1, a description is now given of abasic image forming operation of the image forming apparatus 1.

When a print job starts, electrostatic latent images are formed on thesurfaces of the photoconductors 32 of the process cartridges 31Y, 31C,31M, and 31Bk, according to single color image data, that is, yellow,cyan, magenta, and black image data, respectively, generated by colorseparation of a desired full-color image. The developing devices 34supply toner to the electrostatic latent images thus formed on thephotoconductors 32 with the developing rollers 36, to render theelectrostatic latent images visible as toner images.

The drive roller 41 of the transfer device 4 rotates in acounterclockwise direction in FIG. 1 to rotate the intermediate transferbelt 43 in a direction indicated by arrow A. A power supply applies aconstant voltage or a constant current control voltage having a polarityopposite a polarity of the toner to the primary transfer rollers 45 togenerate a transfer electric field at each primary transfer nip betweenthe primary transfer roller 45 and the corresponding photoconductor 32.The transfer electric fields generated at the primary transfer nipstransfer the yellow, magenta, cyan, and black toner images from thephotoconductors 32 onto the intermediate transfer belt 43 so that theyellow, magenta, cyan, and black toner images are superimposedsuccessively on the intermediate transfer belt 43. Thus, a full-colortoner image is formed on the outer circumferential surface of theintermediate transfer belt 43. The photoconductor cleaning blade 35removes residual toner, which fails to be transferred to theintermediate transfer belt 43 and therefore remains on thephotoconductors 32, from the photoconductors 32. The waste tonercontainer 47 receives such residual toner.

In the meantime, when the print job starts, the sheet feeding roller 52of the sheet feeder 5 disposed in the lower portion of the image formingapparatus 1 is rotated to feed a recording medium P from the tray 51toward the pair of registration rollers 61 through the conveyancepassage 6. Then, the pair of registration rollers 61 feeds the recordingmedium P toward the secondary transfer nip between the secondarytransfer roller 46 and the drive roller 41 at a predetermined time.

A transfer voltage having a polarity opposite a polarity of the chargedtoner contained in the full-color toner image formed on the intermediatetransfer belt 43 is applied to the secondary transfer roller 46, therebygenerating a transfer electric field to transfer the full-color tonerimage onto the recording medium P from the intermediate transfer belt 43at the secondary transfer nip. More specifically, yellow, magenta, cyan,and black toner images are transferred onto the recording medium P fromthe intermediate transfer belt 43 at once.

The cleaning blade 44 removes residual toner, which fails to betransferred to the recording medium P and therefore remains on theintermediate transfer belt 43, from the intermediate transfer belt 43.The waste toner container 47 receives such residual toner, e.g., by ascrew and through the toner conveying tube.

The recording medium P bearing the full-color toner image is conveyed tothe fixing device 7. The fixing device 7 applies heat and pressure tothe recording medium P with the fixing roller 72 heated by the heater 71and the pressing roller 73, thereby fixing the full-color toner imageonto the recording medium P. The recording medium P is separated fromthe fixing roller 72 after the full-color toner image is fixed onto therecording medium P, and conveyed by a pair of conveyance rollers towardthe pair of ejection rollers 81 of the ejection device 8. Then, the pairof ejection rollers 81 ejects the recording medium P onto the ejectiontray 82.

Thus, the operation of forming a full-color image on the recordingmedium P is conducted. Alternatively, the image forming operation may beconducted using any one of the process cartridges 31Y, 31C, 31M, and31Bk to form a monochrome image, or using two or three processcartridges 31 to form a two or three-color image, respectively.

Usually, such image forming apparatuses include drivers and drivetransmission units that transmit driving forces from the drivers, todrive components of the image forming apparatuses to conductpredetermined operations such as rotating photoconductors, sheetfeeding, and image reading, during image forming processes.

However, vibration of such drivers may be also transmitted, which mayadversely affect image quality and cause noise problems. Specifically,the image forming apparatuses include a number of internal componentsmechanically connected to each other. When receiving driving forces fromthe drivers, the internal components vibrate and generate noise.

To reduce such noise, for example, a comparative drive transmission unit20 shown in FIG. 7 includes a motor 200, a drive shaft 201 connected tothe motor 200, a first external gear 202, a first internal gear 203, atop surface 203 a, a second external gear 204, a second internal gear205, an ejection roller shaft 206, a shaft 210, and a frame 211. As themotor 200 rotates, the first external gear 202 rotates about the driveshaft 201, thereby transmitting a driving force to the first internalgear 203 meshing with the first external gear 202. As the first internalgear 203 rotates about the shaft 210, the second external gear 204rotate. Since the second external gear 204 meshes with the secondinternal gear 205, the second internal gear 205 rotates about theejection roller shaft 206. Accordingly, the driving force is transmittedto the ejection roller shaft 206.

The external gears (first and second external gears 202 and 204) meshwith the internal gears (first and second internal gears 203 and 205),respectively, harder than external gears meshing with each other.Accordingly, the driving force is stably transmitted.

In addition, meshing faces between the external gears and the internalgears are covered by the first internal gear 203 and the frame 211 or bythe second internal gear 205 and the top surface 203 a of the firstinternal gear 203, thereby containing noise at the meshing faces.

However, in the comparative drive transmission unit 20, the rotatinginternal gears are not fixed except at their inner circumferentialsurfaces meshing with the external gears. Therefore, the internal gearshave relatively low vibration resistance, and may easily vibrate whenreceiving the driving force. Relatively large vibration of the internalgears may hamper the internal gears from accurately transmitting thedriving force to other components such as an ejection roller. Inaddition, vibration of the internal gears may generate relatively loudnoise.

By contrast, drive transmission units according to embodiments of thisdisclosure accurately transmit a driving force while reducing noise.

The following describes such drive transmission units according toembodiments of this disclosure.

Referring now to FIGS. 2A and 2B, a description is given of a drivetransmission unit 10A according to a first embodiment. FIG. 2A is aschematic sectional view of the drive transmission unit 10A.

The drive transmission unit 10A includes, e.g., a motor 100 serving as adriver source, a motor gear 101, which is a motor shaft, serving as afirst member, a drive transmitting member 102, a first output gear 103,and a rotary shaft 104 as a shaft of the drive transmitting member 102.A driving force of the motor 100 is transmitted to the first output gear103 via the motor gear 101 and the drive transmitting member 102, andfurther transmitted to a driving target.

The drive transmitting member 102 includes a bottom part 102 a, acircular transmitting part 102 b, and circular stiffening ribs 102 c and102 e serving as projecting parts. The bottom part 102 a is intersectedby the rotary shaft 104. The transmitting part 102 b extends from thebottom part 102 a axially along the rotary shaft 104, which is a shaftof the drive transmitting member 102, while coaxial with the rotaryshaft 104. The stiffening ribs 102 c and 102 e are also coaxial with therotary shaft 104, while projecting from the bottom part 102 a axiallyalong the rotary shaft 104 in opposite directions. The stiffening ribs102 c and 102 e have different diameters from each other.

The diameters of the transmitting part 102 b, the stiffening rib 102 c,and the stiffening rib 102 e, each coaxial with the rotary shaft 104 aretransmitting part 102 b>stiffening rib 102 c>stiffening rib 102 e.

FIG. 2B is a vertical sectional view of the drive transmission unit 10Aalong a line J1 shown in FIG. 2A. As shown in FIG. 2B, the stiffeningrib 102 c is positioned between the transmitting part 102 b and thestiffening rib 102 e in an arbitrary direction on a plane (i.e., sheetface of FIG. 2B) perpendicular to an axial direction of the rotary shaft104. In other words, the transmitting part 102 b, the stiffening rib 102c, and the stiffening rib 102 e are dimensioned so that K1 and K2 areequal, where, as shown in FIG. 2B, the K1 is a difference between aninner diameter of the transmitting part 102 b and an outer diameter ofthe stiffening rib 102 c, and the K2 is a difference between an innerdiameter of the stiffening rib 102 c and an outer diameter of thestiffening rib 102 e.

The transmitting part 102 b includes an internal toothed surface 102 don its inner circumferential surface to mesh with other members such asthe motor gear 101 and the first output gear 103. The motor gear 101 andthe first output gear 103 serve as first members that mesh with theinternal toothed surface 102 d. Specifically, the internal toothedsurface 102 d meshes with a tooth part 101 a provided on an outercircumferential surface of the motor gear 101, via a meshing face B. Atthe same time, the internal toothed surface 102 d meshes with a toothpart 103 a provided on an outer circumferential surface of the firstoutput gear 103, via a meshing face C. The meshing faces B and C faceeach other with the rotary shaft 104 interposed therebetween.

The driving force of the motor 100 is transmitted to the motor gear 101,and further transmitted to the transmitting part 102 b of the drivetransmitting member 102 via the meshing face B. Receiving the drivingforce, the drive transmitting member 102 rotates about the rotary shaft104 to transmit the driving force to the first output gear 103 via themeshing face C.

The stiffening ribs 102 c and 102 e strengthen the drive transmittingmember 102, and suppress vibration of the drive transmitting member 102while the drive transmitting member 102 is rotating about the rotaryshaft 104 to transmit the driving force to the first output gear 103.

As described above, the stiffening ribs 102 c and 102 e have differentdiameters from each other. If the stiffening ribs 102 c and 102 e hadthe same diameter, stress would concentrate at the bases of thestiffening ribs 102 c and 102 e and weaken them as the drivetransmitting member 102 vibrates. In such a case, the stiffening ribs102 c and 102 e might not sufficiently strengthen the drive transmittingmember 102.

By contrast, in the present embodiment, the stiffening ribs 102 c and102 e have different diameters from each other to strengthen the drivetransmitting member 102 sufficiently to suppress the vibration of thedrive transmitting member 102. Reducing the vibration of the drivetransmitting member 102 allows the drive transmitting member 102 toaccurately transmit the driving force, while reducing noise.

More specifically, after receiving the driving force from the motor 100via the motor gear 101, the drive transmitting member 102 accuratelytransmits the driving force to the first output gear 103 because thevibration of the drive transmitting member 102 is suppressed. Reductionof the vibration of the drive transmitting member 102 reduces noise.

In the present embodiment, the bottom part 102 a and the transmittingpart 102 b cover the meshing faces B and C. Accordingly, noise generatedfrom the meshing faces B and C is contained, thereby reducing noise.

As shown in FIG. 2A, the meshing faces B and C face each other with therotary shaft 104 interposed therebetween. In other words, the drivetransmitting member 102 has meshing faces on both sides (i.e., upper andlower sides in FIG. 2A). Thus, the vibration of the drive transmittingmember 102 is suppressed more efficiently than a drive transmittingmember having only one side provided with a meshing face and the otherside unfixed.

In FIG. 2A, H represents a width of the stiffening rib 102 c axiallyalong the rotary shaft 104. Similarly, G represents a width of thestiffening rib 102 e axially along the rotary shaft 104. F represents aface width of the internal toothed surface 102 d. In the presentembodiment, the width H or the width H+G is longer than the face widthF. The internal toothed surface 102 d receives vibration from the motorgear 101 in the face width F. The vibration is then transmitted to thestiffening ribs 102 c and 102 e positioned inward from the internaltoothed surface 102 d. Accordingly, the stiffening ribs 102 c and 102 ealso vibrate. The width H+G is longer than the face width F andsufficient to reduce vibration that the stiffening ribs 102 c and 102 ereceive per unit width, thereby strengthening the drive transmittingmember 102.

In addition, each of the stiffening ribs 102 c and 102 e has asufficient width to reduce a relative length of the internal toothedsurface 102 d projecting from the bottom part 102 a, resulting in lowinclination. Accordingly, the inclination of the internal toothedsurface 102 d is reduced when the drive transmitting member 102 vibrateswhile rotating about the rotary shaft 104.

In the present embodiment, the height (i.e., width) G of the stiffeningrib 102 e is equal to the height F of the transmitting part 102 b (i.e.,face width of the internal toothed surface 102 d). Alternatively, theheight G may be shorter than the height F.

Referring now to FIG. 3, a description is given of a drive transmissionunit 10B according to a second embodiment. FIG. 3 is a schematicsectional view of the drive transmission unit 10B.

In the second embodiment, the drive transmission unit 10B includes adrive transmitting member 102 that includes a circular peripheral wall102 g. The peripheral wall 102 g is coaxial with a rotary shaft 104,while projecting from a bottom part 102 a in a direction opposite adirection in which a transmitting part 102 b projects from the bottompart 102 a. The peripheral wall 102 g has a larger diameter than thetransmitting part 102 b, the circular stiffening rib 102 c and thecircular stiffening rib 102 e. The peripheral wall 102 g serves as anouter circumferential surface of the drive transmitting member 102.

In addition, the peripheral wall 102 g includes an external toothedsurface 102 f on its outer circumferential surface. The drivetransmission unit 10B also includes a second output gear 105 serving asa second member that meshes with the external toothed surface 102 f. Theexternal toothed surface 102 f meshes with a tooth part 105 a providedon an outer circumferential surface of the second output gear 105, via ameshing face D. The meshing face D between the drive transmitting member102 and the second output gear 105 faces a meshing face B between thedrive transmitting member 102 and a motor gear 101 with the rotary shaft104 interposed therebetween.

In the drive transmission unit 10B, the drive transmitting member 102transmits a driving force from a motor 100 to both a first output gear103 and the second output gear 105. In addition, the drive transmittingmember 102 has meshing faces having tooth parts on its inner and outercircumferential surfaces.

Referring now to FIG. 4, a description is given of a drive transmissionunit 10C according to a third embodiment. FIG. 4 is a schematicsectional view of the drive transmission unit 10C.

In the third embodiment, the drive transmission unit 10C includes adrive transmitting member 102 that includes a circular peripheral wall102 g. The peripheral wall 102 g is coaxial with a rotary shaft 104,while projecting from a bottom part 102 a in opposite directions axiallyalong the rotary shaft 104.

The peripheral wall 102 g has an external toothed surface 102 f. Thebottom part 102 a is located in the center of the external toothedsurface 102 f in an axial direction of the rotary shaft 104.Accordingly, when the external toothed surface 102 f and a tooth part105 a mesh via a meshing face D and generate vibration, the vibration istransmitted equally in the opposite directions from the bottom part 102a axially along the rotary shaft 104. As a result, vibration of thedrive transmitting member 102 is kept stable, and therefore, the drivetransmitting member 102 accurately transmits the driving force from amotor 100.

Referring now to FIG. 5, a description is given of a drive transmissionunit 10D according to a fourth embodiment. FIG. 5 is a schematicsectional view of the drive transmission unit 10D.

In the fourth embodiment, the drive transmission unit 10D includes adrive transmitting member 102 that includes a transmitting part 102 b.The transmitting part 102 b has an external toothed surface 102 h on itsouter circumferential surface. The external toothed surface 102 h mesheswith a tooth part 101 b provided on an inner circumferential surface ofa motor gear 101 via a meshing face B. The drive transmitting member 102also includes a peripheral wall 102 g that has an internal toothedsurface 102 j on its inner circumferential surface. The internal toothedsurface 102 j meshes with a tooth part 105 a provided on an outercircumferential surface of a second output gear 105 via a meshing faceD. Thus, unlike the first through third embodiments, the motor gear 101has a tooth part on its inner circumferential surface, the transmittingpart 102 b has an external toothed surface, and the peripheral wall 102g has an internal toothed surface.

In the fourth embodiment, the peripheral wall 102 g is a circularprojecting part. In other words, the peripheral wall 102 g is coaxialwith a rotary shaft 104, while projecting from a bottom part 102 aaxially along the rotary shaft 104. As described above, the peripheralwall 102 g has the internal toothed surface 102 j. Accordingly, theperipheral wall 102 g serves as a transmitting part that transmits adriving force. As shown in FIG. 5, the peripheral wall 102 g has alarger diameter than a stiffening rib 102 e, which is also a circularprojecting part coaxial with the rotary shaft 104 while projecting fromthe bottom part 102 a.

In the fourth embodiment, the drive transmission unit 10D does notinclude a first output gear 103. Alternatively, as in the thirdembodiment, the drive transmission unit 10D may include the first outputgear 103 that faces the motor gear 101 with the rotary shaft 104interposed therebetween, to mesh with the drive transmitting member 102.In such a case, a tooth part 103 a of the first output gear 103 mesheswith the external toothed surface 102 h, instead of the internal toothedsurface 102 d of the drive transmitting member 102 described above inthe first embodiment, for example.

Referring now to FIGS. 6A and 6B, a description is given of a drivetransmission unit 10E according to a fifth embodiment. FIG. 6A is aschematic sectional view of the drive transmission unit 10E. FIG. 6B isa vertical sectional view of the drive transmission unit 10E along aline J2 shown in FIG. 6A.

In the fifth embodiment, the drive transmission unit 10D includes adrive transmitting member 102 that includes a peripheral wall 102 g.Although the peripheral wall 102 g does not have either the externaltoothed surface 102 f or the internal toothed surface 102 j as describedabove, a belt 106 is wound around the peripheral wall 102 g. The belt106 is also wound around a driving target on a side (upper side in FIGS.6A and 6B) opposite the peripheral wall 102 g.

As the drive transmitting member 102 rotates about a rotary shaft 104,the peripheral wall 102 g also rotates about the rotary shaft 104,thereby transmitting a driving force to the driving target via the belt106.

According to the above-described embodiments, a drive transmission unit(e.g., drive transmission unit 10A) includes a drive transmitting member(e.g., drive transmitting member 102). The drive transmitting memberincludes a bottom part (e.g., bottom part 102 a) and a circulartransmitting part (e.g., transmitting part 102 b) that includes aninternal toothed surface (internal toothed surface 102 d). The internaltoothed surface meshes with another member (e.g., motor gear 101) via ameshing face (e.g., meshing face B) to transmit a driving force. Themeshing face is surrounded by the transmitting part and the bottom partto contain vibration. The drive transmitting member also includescircular projecting parts projecting from the bottom part in oppositedirections along an axial direction of the drive transmitting member, tostiffen the drive transmitting member and dampen vibration of the drivetransmitting member. The circular projecting parts have differentdiameters to prevent stress from concentrating at the projecting parts,thereby strengthening the drive transmitting member and suppressingvibration of the drive transmitting member. Accordingly, the drivetransmission unit accurately transmits the driving force while reducingnoise.

It is to be noted that the number of constituent elements and theirlocations, shapes, and so forth are not limited to any of the structurefor performing the methodology illustrated in the drawings.

For example, the image forming apparatus according to the embodiment ofthis disclosure is not limited to the image forming apparatus 1 thatforms a color image. Alternatively, the image forming apparatus may bean image forming apparatus that forms a monochrome image. The imageforming apparatus may be a copier, a printer, a facsimile machine, or amultifunction peripheral having two or more of copying, printing, andfacsimile capabilities.

This disclosure has been described above with reference to specificembodiments. It is to be noted that this disclosure is not limited tothe details of the embodiments described above, but variousmodifications and enhancements are possible without departing from thescope of the invention. It is therefore to be understood that thisdisclosure may be practiced otherwise than as specifically describedherein. For example, elements and/or features of different illustrativeembodiments may be combined with each other and/or substituted for eachother within the scope of this disclosure.

What is claimed is:
 1. A drive transmission unit comprising: a drivesource; and a rotatable drive transmitting member to transmit a drivingforce from the drive source, the rotatable drive transmitting membercomprising: a circular recessed part including a tooth portion of aninner circumferential surface of the circular recessed part; a firstcircular projecting part dividing the circular recessed part into aplurality of recessed portions in a radial direction of the drivetransmitting member, the first circular projecting part projecting in afirst direction perpendicular to a direction of rotation of the drivetransmitting member; and a second circular projecting part projecting ina second direction opposite the first direction, wherein an outerdiameter of the second circular projecting part is relatively smallerthan an inner diameter of the drive transmitting member and an innerdiameter of the second circular projecting part is relatively largerthan an outer diameter of the first circular projecting part, andwherein a difference between the inner diameter of the second circularprojecting part and the outer diameter of the first circular projectingpart is substantially equal to a difference between the inner diameterof the drive transmitting member and the outer diameter of the secondcircular projecting part.
 2. The drive transmission unit according toclaim 1, wherein the drive transmitting member further comprises acircular peripheral wall extending from a bottom part in the seconddirection along an axial direction of the drive transmitting member, andwherein the circular peripheral wall comprises an external toothedsurface on an outer circumferential surface of the circular peripheralwall to mesh with a second member.
 3. The drive transmission unitaccording to claim 1, wherein the drive transmitting member furthercomprises a circular peripheral wall extending from a bottom part inboth the first direction and the second direction along an axialdirection of the drive transmitting member, and wherein the circularperipheral wall comprises an external toothed surface on an outercircumferential surface of the circular peripheral wall to mesh with asecond member.
 4. The drive transmission unit according to claim 3,wherein the bottom part is positioned at an axial center of the externaltoothed surface in the axial direction of the drive transmitting member.5. The drive transmission unit according to claim 1, further comprisinga belt, wherein the drive transmitting member further comprises acircular peripheral wall extending from a bottom part in an axialdirection of the drive transmitting member; and wherein the belt iswound around an outer circumferential surface of the circular peripheralwall to transmit the driving force from the drive source.
 6. The drivetransmission unit according to claim 5, wherein the circular peripheralwall extends from the bottom part in the second direction along theaxial direction of the drive transmitting member.
 7. The drivetransmission unit according to claim 5, wherein the circular peripheralwall extends from the bottom part in both the first direction and thesecond direction along the axial direction of the drive transmittingmember.
 8. The drive transmission unit according to claim 1, furthercomprising a shaft, wherein the tooth portion of the innercircumferential surface of the circular recessed part meshes with one ormore members via a plurality of meshing points, and wherein at least twoof the plurality of meshing points are opposite each other with arotation center of the drive transmitting member interposed between theat least two of the plurality of meshing points.
 9. An image formingapparatus comprising the drive transmission unit according to claim 1.10. An image forming apparatus comprising the drive transmission unitaccording to claim
 8. 11. The drive transmission unit of claim 1,wherein the first and second circular projecting parts are circularstiffening ribs.